1. Field of the Invention
This invention is in the field of hydraulic fracturing. More particularly, it is concerned with the fracturing of the rocks in deep boreholes in the earth. Still more particularly, it is concerned with the fracturing of oil wells.
Still more particularly, it concerns the art of generating high pressure hydraulic pulses in deep boreholes and using these pressure pulses to produce fractures using less pump power than is normally now required.
Still more particularly, it concerns the use of sonic detecting means to detect seismic waves generated at the fracture by these pressure pulses, to determine the azimuth and length of the fracture.
2. Description of the Prior Art
The process of hydraulic fracturing (also called "hydrofracing" or "fracturing") of oil and gas wells has been in common use over the past 20-25 years, with great economic results. In all of these operations, high pressure liquid pumps are used to pump a selected fluid, generally called a fracturing fluid, which may be an oil or water solution with or without thickening agents and generally including a so-called propping agent, such as sand, etc. All of this art is well known and is taught in textbooks and technical papers and need not be described further.
In the course of the fracturing operation, one or more pumps are connected to a manifold and to a "pipe" (such as drill pipe or tubing) in the well. The pipe is packed off to the wall of the well at a selected depth to apply the hydraulic pressure to a selected portion or zone in the well. This zone can be at the bottom, or at some intermediate depth in the well. The well can be cased (with perforations), or uncased.
The procedure is to build up the pressure and flow rate of the fluid being pumped until a selected hydrostatic pressure is reached at the packed off zone, at which the rock will spontaneously fracture, along a plane of weakness of the rock. When this happens, the hydraulic pressure drops to a lower sustained value.